Nortuy Haven Sanp PLains 579 
the sand under the trees, probably germinate and dry up before 
the radicles can reach a sufficient depth to obtain the necessary 
moisture. In some unpublished investigations Professor J. W. 
Toumey has found that in hard soil the radicle is not able to work 
its way into the soil, but on account of the lightness of the acorn 
it is tumbled about on the surface. The shells form a coating on 
the sand under the oaks, and with fallen leaves and other waste 
vegetable matter that is blown about, help to form a thin layer of 
_ leaf-mold where not destroyed by fire. 
Under these oaks grows a moss, Polytrichum piliferum, which 
also aids in the formation of soil. The rhizoids hold together the 
upper two inches of sand, thus preventing it from shifting, and the 
plant doubtless has some influence on the retention of the mois- 
ture. Therefore certain plants grow in company with the moss 
which do not appear on other portions of the sand area and which 
probably could not persist there. The scrub-oak (Quercus nana) 
also grows at North Haven and there are several specimens of 
dwarfed chestnut trees. 
Certain areas on the North Haven tract are covered with 
reindeer moss, Cladonia rangiferina, and where this lichen be- 
comes established other plants soon spring up. It holds the sand 
from shifting, and leaves and other portions of plants blown about 
by the winds finally lodge upon it creating a thin layer of slowly 
decaying vegetable matter. The surface being undisturbed and 
the leaf-mold retaining a portion of the moisture that formerly es- 
caped through evaporation, seeds that fall upon this area are able 
to germinate and grow. Sweet fern (Comptonia peregrina) covers 
quite an area near the reindeer moss and may perhaps follow 
it as the next stage in the development of a forest growth on 
this land. 7 
Much of the accumulating humus on the North Haven tract 
has been destroyed by fires probably started by sparks emitted 
from passing engines. Leaves and dry grass have been burned in 
this manner and in one locality the sedges collected show the 
result of such fires; the old culms had been burned off level with 
the sand and from the blackened base the new growth had been 
pushed out. Fires cannot sweep over the whole area for lack of 
combustible material, yet the dry leaves which have lodged be- 
